Setting up the conversion functions:

# From Light Values to LUX
lv2lux <- function(lv) (2^lv)*2.5  

# From LUX to Light Values
lux2lv <- function(lux) log(lux/2.5, 2)

Plotting the conversion function:

# Interactive plot

library(plotly, quietly = T, verbose = F, warn.conflicts = F)

lv <- seq(3,15,.5)
lux <- lv2lux(lv)
crv <- data.frame(Light_Value = lv, LUX = lux)
plot_ly(crv, x = ~lv, y = ~lux,
        type = 'scatter', mode = 'lines')